Heterogeneous photochemistry driving organic aerosols production
Résumé
Christian George Université de Lyon; université Lyon 1; CNRS, UMR5256, IRCELYON, Institut de recherches sur la catalyse et lenvironnement de Lyon, Villeurbanne, F-69626, France. Reliable modeling predictions require reliable fundamental scientific knowledge of the underlying processes. Despite extensive observational data accumulated to date, aerosols still pose key uncertainties in our understanding. Specifically, major gaps exist in the understanding of the physicochemical pathways that lead to aerosol growth in the atmosphere and to changes in their properties while in the atmosphere. Traditionally, the driving forces for particle growth are attributed to condensation of condensable species following atmospheric oxidation of volatile species by gaseous oxidants. The present study presents experimental evidence of an unaccounted-for new photo-induced pathway for particles growth in the absence of a gas phase. Heterogeneous reactions activated by light lead to fast uptake of non-condensable VOCs at the surface of particles only when traces of a photosensitizer were in the aerosol seed. Under such conditions, size and mass increase, as well as change s in the chemical composition of the aerosol are observed upon exposure to volatile organic compounds such as terpenes and near-UV irradiation. Experimentally determined growth rate values match field observations, suggesting that this photochemical process can provide a new unaccounted for pathway for atmospheric particle growth and should be considered by models.